Rim-fire improvement



June 28, 1966 c. L. HUBBARD 3,257,892

RIM-FIRE IMPROVEMENT Filed July 17, 1 964 H 5 I q/i FJG'I FIG-2 INVENTOR. CHARLES L HUBBARD A 7' TORNEV United States Patent 3,257,892 RllVI-FIRE IMPROVEMENT Charles L. Hubbard, Roxana, Ill., assignor to 01in This invention relates to ammunition and more specifically to an improved rim-fire cartridge and method of priming of rim-fire cartridges.

These well known cartridges have a one-piece case including a head portion characterized by a hollow rim, the internal trough of which extends all around next to the base and contains a primer composition. In manufacture of such cartridges, a cup-like shell blank of desired length heretofore has been held in a die on a punch having a shoulder engaging the mouth of the blank so that the blank held in this way may be impacted in the die to upset, flatten, and enlarge the closed head of the blank until the final hollow rim configuration is made as shown in Us. Patent No. 167,005. Thereafter, the priming composition, which is a pulverulent mixture usually with just enough moisture for coherency, is positioned in the hollow rim by any suitable means such as a spinning punch like that shown in US. Patent Nos. 887,508 and 2,313,- 265. When the primed shell is finally loaded with a propellant powder and is closed at the mouth by either a bullet or by a wad or in any other suitable way, the rimfire ammunition is ready for a firearm. In use, the loaded cartridge is received with its cylindrical body in a cartridge chamber in the gun barrel and the front face of the rim adjacent the body engages the gun barrel while the rim is received in the conventional head space portion of the gun, thereby adapting the cartridge for percussive ignition. The thickness of the cartridge head in the rim is nearly equal to but somewhat less than the gun head space which is that longitudinal distance between the gun barrel chamber mouth and the bolt face occupied by (1) the thickness of metal at the front of the rim, (2) the thickness of metal at the base of the rim, and (3) the intervening thickness of priming composition.

In the event of any nonuniform-ity in the case thickness and bulk density of mixture used, variations occur in the placement of the composition in the rim cavity. This detracts from the reliability and uniformity of ignition and requires the use of impact energy on the high side.

The head space for the cartridge rim must be held at a conventional value in firearms. The impact of the firing pin on the back face of the rim is likewise a conventional matter. These conventional features of firearm and cartridge construction impose limitations that cannot be altered.

Operated on in a given range of standard blows obtainable from firing pins and placed in a standard head space, the sensitivity of the priming mixture must be adequate to insure ignition regardless of normal variations in head space, in firing pin impact, in cartridge case metal hardness, in cartridge case metal thickness, and in other factors such as moisture which affect the ignition.

The present invention provides a primed head structure in a rim-fire cartridge improved in primer sensitivity and initiation reliability by mechanical compression of the cartridge case rim after the placement of the charge of priming mixture in the rim cavity. The resulting compaction of the priming mixture is in addition to whatever kind of packing occurs during the usual mixture feeding operation such as the centrifugal operation of spinning in the mixture. The effective compaction occurs after the mixture is fed into the partially formed rim.

By effective compaction is meant that final compaction which permits more reliable initiation at lower energy levels of impact with less variation than heretofore occurs with known mixture positioning. Compaction reduces the initial volume.

Compaction according to this invention is done by compressing the cartridge case rim either after or in increments during mixture positioning in the rim. -Such positioning may be by any suitable means not restricted to conventional spin. feed. This compression reduces the head space height or thickness of the rim longitudinally to its final finished thickness and the resulting compaction of the priming mixture consolidates and homogenizes it with more uniform circumferential distribution.

Various features and advantages of the invention will be understood from this description of a specific embodiment with reference to a drawing of the same in which:

FIG. 1 is a fragmentary side elevational view showing in cross section the closed end in the lower part of a rimfire cartridge case with a partially formed rim being loaded with priming mixture in apparatus part of which is also shown; and

FIG. 2 is a fragmentary side elevational view showing the same lower part of the cartridge case after the rim has been compressed to the final thickness and with the mixture compacted by the associated apparatus shown.

In FIG. 1 the partially finished catridge supported between the bunter 2 and the heading die 3 has a tubular body 5 and has integrally formed therewith a rim bulge 6 of longitudinal height H defining a rim cavity into which spinner 7 has tightly compacted a charge 8 of a suitable priming mixture distributed centrifugally by the spinner from a pellet of the mixture introduced into the partially headed cartridge shell. The volume of the rim bulge cavity is about equal to the volume of the pellet and formed so that the mixture is placed in tightly enough to remain in place and is confined sufiiciently to retain its position even during compaction.

In FIG. 2 heading die 2 has compressed the bulge against hunter 3 to form a finished rim 10 of final finished thickness T about equal to but not exceeding the head space in which the rim is to be received. This produces in the rim the finally compacted priming ring 11. Before this stage of operation the spinner may be withdrawn. Alternatively, the spinner may remain as shown either motionless or still spinning. Furthermore, the spinner at this stage may be replaced by a fiat ended punch seated snugly on the base 9 of the cartridge shell, where the highest degree of confinement is desired. Such a punch may be bevel edged. In any event, the priming mixture is always compacted and distributed quite uniformly as an annulus at the rim in the most eflicient state and form for ignition; this occurs as the base portion and gun barrel engaging portion of rim 10 are squeezed to rim thickness T and a volume which does not materially exceed the volume of the finally compacted mixture, less than that of the pellet.

Any priming composition amenable to improvement in sensitivity by compaction in accordance with this invention is contemplated. A wet priming mixture is preferably employed but the same benefits are obtained with dry mixtures provided compaction is done with precautions taken with regard to the increased probability of the accidental ignition which is likely to occur during dry loading of any priming composition. One preferred type of composition is based on the use of lead styphnate together with barium nitrate and other ingredients usually included in the mixture. The styphnate may be of the type disclosed in US. Patent No. 2,150,653 and/or of the type disclosed in US. Patent No. 1,942,274. Barium nitrate or its equivalent is included as shown, for example,

TABLE Before Com- After Compression pression Average Height In Inches 5. 24 4. 22 Standard Deviation 0.77 O. 60

From this example it is seen that compression of the priming mixture after the usual loading in the partially formed rim increases the sensitivity measurably and makes the placement of the mixture more uniform in the rim cavity. The preformed cavity is such as to receive and retain in position for compaction an adequate supply of the mixture.

The degree of compaction determines the extent of improved sensitivity. Among the limitations on compaction are the final finished height of the rim with respect to the available head space, the sufiiciency of mixture quantity in the initiation area for propagation, and the inception of initiation during primer loading. Since the final finished height of the rim is substantially constant, the degree of compaction may be stated in terms of the percentage of reduction of the rim overall height with reference to the height or thickness of initial bulge at the rim. The data set forth in the above-noted table Was obtained with a degree of compression of from about 30 to about 35%. The permissible maximum compaction varies of course with the composition of the priming mixture, its state resulting from its initial positioning, and its moisture content. The optimum degree of compaction is reached by a process of trial and error determined by the operators setting of the priming presses in cooperation with laboratory measurements of sensitivity.

Although the foregoing is a description of what is now believed to be the preferred structure and procedure, it will be understood that those skilled in the art may make changes and modifications Without departing from the spirit and scope of this invention as set forth in the appended claims.

What is claimed is:

1. In the manufacture of rim-fire propellant cartridges the method of increasing the sensitivity and uniformity of the priming composition to percussive ignition comprising providing a cartridge having a tubular body and anintegral head including a closed base and an unfinished rim having a thickness in excess of the final head space, transferring a volume of said composition to position it in the form of an annulus into 'the rim leaving said base substantially free from said composition, and compressing the rim longitudinally and the composition positioned therein by flattening the rim to simultaneously obtain a final finished rim thickness, a reduction in said volume, and composition compaction characterized by an increased sensitivity to and uniformity of ignition.

2. The method of claim 1 wherein transferring occurs by insertion of a pellet of priming composition on the base followed by centrifugal feeding into the rim.

3. In the manufacture of rim-fire propellant cartridges, the method comprising providing a cartridge case having a tubular body and an integral head including a closed base and a rim, said rim defining a priming composition cavity, positioning a volume of priming composition within said cavity, and reducing the thickness of said rim to compact said composition.

References Cited by the Examiner UNITED STATES PATENTS 67,189 7/1867 Goff 8617 2,981,137 4/1961 Sahlin 8632 3,019,688 2/1962 Hunt 8623 OTHER REFERENCES Military Explosives, TM-9-1910, TO-l 1A-134, April 1955, pp. 113-114.

Cartridge Manufacture, by Hamilton, The Industrial Press, 1st edition, 1916, uf/740/H3, pp. 161 req.

Smokeless Shotgun Powders, by Coxe Du Pont Publication, 1933, pp. 37-59 required.

BENJAMIN A. BORCHELT, Primary Examiner.

R. F. STAHL, Assistant Examiner. 

1. IN THE MANUFACTURE OF RIM-FIRE PROPELLANT CARTRIDGES THE METHOD OF INCREASING THE SENSTIVITY AND UNIFORMLY OF THE PRIMING COMPOSITION TO PERCUSSIVE IGNITION COMPRISING PROVIDING A CARTRIDGE HAVING A TUBULAR BODY AND AN INTEGRAL HEAD INCLUDING A CLOSED BASE AND AN UNFINISHED RIM HAVING A THICKNESS IN EXCESS OF THE FINAL HEAD SPACE, TRANSFERRING A VOLUME OF SAID COMPOSITION TO POSITION IT IN THE FORM OF AN ANNULUS INTO THE RIM LEAVING SAID BASE SUBSTANTIALLY FREE FROM SAID COMPOSITION, AND COMPRESSING THE RIM LONGITUDINALLY AND THE COMPOSITION POSITIONED THEREIN BY FLATTENING THE RIM TO SIMULTANEOUSLY OBTAIN A FINAL FINISHED RIM THICKNESS, A REDUCTION IN SAID VOLUME, AND COMPOSITION COMPACTION CHARACTERIZED BY AN INCREASED SENSITIVITY TO AND UNIFORMITY OF IGNITION. 